1. Field of the Invention
The present invention relates to an apparatus for detecting a position appointed by a position appointing magnetism generator. More particularly, the invention is concerned with a position detecting apparatus of the type mentioned above, capable of detecting the appointed position by making use of a magnetostrictive vibration wave which is propagated through a magnetostrictive transmission medium, without requiring any exchange of timing signal between the apparatus and the magnetism generator.
2. Description of the Prior Art
A typical example of the position detecting apparatus of the kind described is shown in, for example, Japanese Patent Publication No. 32668/1981. In this known apparatus, an instantaneous change of magnetic field is generated by a position appointing magnetism generator and is propagated in the form of magnetostrictive vibration wave through a magnetostrictive transmission medium to reach a detecting coil disposed at the distal end of the medium. The position appointed by the position appointing magnetism generator is detected by measuring and processing with a processing unit the length of time from the moment at which the instantaneous change in magnetic field is generated until the moment at which the magnetostrictive vibration wave is detected by the detecting coil. In this known apparatus, therefore, it is necessary to connect the position appointing magnetism generator to the processing unit through a signal line, in order to inform the processing unit of the timing at which the instantaneous change in the magnetic field is generated. Consequently, the mobility, as well as the handling, of the position appointing magnetism generator is restricted undesirably. For this reason, the known position detecting apparatus has been able to find only limited use.
This problem is serious particularly when the detection of position has to be made over a planar surface because in such a case the position appointing magnetism generator has to move over a wide area.